In the given figure, there is a circuit of potentiometer of length \( AB = 10 \, \text{m} \). The resistance per unit length is \( 0.1 \, \Omega / \text{cm} \). Across \( AB \), a battery of emf \( E \) and internal resistance '\( r \)' is connected. The maximum value of emf measured by this potentiometer is:
